The present invention relates to the field of microcapsules (MCs) and, more particularly, to the field of microcapsules where light triggers a capsule response.
Release of selected chemical species at selected spatial positions at selected times is of central importance in biology, chemistry, and materials science. As an example, a time-release capsule of a certain medication, taken orally, accomplishes time/space release in a crude but effective way. Of great utility is a mechanism to reliably, stably, and carefully transport “packaged” chemicals via a liquid stream and release the chemicals from the package via “remote control” at a given location at a given time.
While liquid filled microcapsules (e.g., see ref 1) are widespread with applications as varied as carbonless copy paper, agrochemicals, or self-healing polymers (e.g., see ref. 2), remote triggering of content release is not common for free-flowing microcapsules. Langer et al. have described the remote release of chemicals from a microchip by dissolution of a polymer membrane triggered by application of an electric potential (see ref. 3). More commonly, release is induced through crushing or the application of other forms of mechanical stress (e.g., see refs. 1 and 2).
Triggering the release of the contents of MCs by light is attractive as light can easily address a small object or blanket an entire surface. In early work, Masuhara et. al, have reported the escape of toluene/pyrene droplets from an optically trapped melamine/formaldehyde microcapsule when irradiated with a second laser that caused ablation of the capsule wall (see ref. 5). Similarly, Au or Ag nanoparticles have more recently been used as optothermal triggers for the breakdown of semi-permeable polyelectrolyte membranes in which the Au or Ag nanoparticles are located in the semi-permeable membrane (see ref. 6).
Carbon nanotubes (CNTs) absorb light across the entire spectrum (e.g., see ref. 7) and efficiently convert the absorbed light into heat (e.g., see ref. 8). Unfortunately, CNTs are poorly soluble in most organic solvents.
The interfacial polymerization of triamines and diacid or triacid chlorides in an oil-in-water emulsion is a technique thoroughly studied by Mathowitz and Cohen (see ref. 9).
The synthesis, characterization, and properties of polyamide walled microcapsules are well documented, as in a series of papers (refs. 4a, 9, and 12a-c) by Mathowitz and Cohen.